When you try to upgrade from Windows Vista to Windows 7, the upgrade fails and your computer rolls back to Windows Vista. This problem may occur for one of the following reasons: A memory issue on the computer;
A hard disk issue on the computer;
Certain third-party drivers are installed on the computer. “A rollback may (…) occur when the third-party driver Sptd.sys is installed on the computer. This driver is distributed with several applications such as Daemon Tools and Alcohol 120%. We recommend that you temporarily uninstall third-party CD/DVD Authoring or Virtualization software that could contain this driver before you upgrade the computer to Windows 7″.